On my old 37 Buick it had a 4.44 rear end from the factory and 8.25/15 tires. From there it went to a 2.73 rear and 28" tall radials and then to an overdrive transmission and 4.11 rear, same tires. Through all these changes the speedometer stayed dead accurate because I have a gps speedometer which I recommend as it does away with gears, cables, and inaccuracy. I had to have mine custom fit in the instrument cluster but as many AD's as there are someone most likely makes a ready to go unit.
